1. Field of the Invention
The present invention relates generally to a transformer of double-insulated type in which a primary and a secondary winding assemblies are assembled to surround coaxially a core assembly in this order. More specifically, the present invention pertains to the double insulated transformer of the above type that has a simplified structure and can easily be assembled.
2. Related Art Description
Among double insulated transformers which meet the Standard of IEC (International Electrotechnical Commission), there has been known a transformer of the type having primary and secondary winding assemblies arranged coaxially in this order around a core assembly, which is referred to as a coaxial-type transformer. In this type of transformer, the primary winding assembly comprises a coil bobbin provided at the center with a through-hole extending axially, into which the center core of the core assembly is inserted. Likewise, the secondary winding assembly comprises a coil bobbin provided at the center with a through-hole extending axially, into which the primary winding assembly is accomodated. The coil bobbins of the primary and secondary winding assemblies have a terminal portion for connecting the outer ends of the coil winding to external lead lines, and both ends of the coil windings and corresponding external lead lines are twisted together and soldered at the respective terminal portions.
In the transformer of the above-mentioned coaxial type, the secondary coil winding of the secondary winding assembly is exposed outwardly, so that it is surrounded by an insulating covering sheet. The terminal portions of the primary and secondary winding assemblies are also exposed, and so covered and protected by another insulating cover in order mainly to prevent operators from accidentally touching the terminals. It is, however, desirable in view of productivity and cost reduction of the transformer that the coverage and protection of those exposed portions can be carried out by utilizing a less number of components and by more simplified assembing operations.
Whereas, in the operations of wiring the coil windings and the external lead lines, both the coil windings and the lead lines are too flexible to remain fixed in their positions by themselves, which causes automatic wiring operation thereof difficult to realize.